Lecture 26 - Human Inherited Sex Linked Traits

Question 1

• Describe why patterns of inheritance are more complicated to study in
humans.

Answer 1

• We don’t choose our mating
partners for the convenience of
biologists.
• The number of children in human
families is relatively small, and the
Mendelian ratios are often
obscured.

Question 2

Describe a pedigree and know how to read a basic pedigree chart.

Answer 2

• Pedigrees are used to look at human patterns of inheritance.

Question 3

• Describe and compare the pedigrees of dominant and recessive disorders.

Answer 3

Dominant disorder:
- rare dominant traits that produce affected offspring normally only have one affected parent.

• For matings in which one parent is affected, roughly half of the offspring will be affected.
• Affected individuals appear in each generation.
• Males and females are equally likely to be affected.

Recessive Disorder:
- Recessive trait may skip one or more generations.

• Males and females are equally likely to be affected.
• Affected individuals can have parents who are not affected.
• Affected individuals often result from mating between relatives.

Question 4

• Describe and compare Incomplete Penetrance and Variable Expressivity.

Answer 4

Incomplete Penetrance:
- Individuals with a genotype
corresponding to a trait do not actually show the phenotype either because of environmental effects or because of interactions with other genes
- Trait is sometimes expressed and sometimes isn’t.

Variable expressivity:
- Phenotype is expressed but with a different degree of severity in
different individuals
- Trait is always expressed, but severity varies.

Question 5

• Define genetic testing and describe the benefits and risks of using this
technology.

Answer 5

• Used to characterize an individual’s genotype
  • Benefits
  Ø Personalized medicine/treatment, informed decisions about
  healthcare
  Ø Better understanding of risks, behaviors
  Ø Feeling less anxious, leading to a better quality of life
  • Risks
  Ø Limited answers
  Ø Physiological/emotional impact
  Ø Privacy issues

Question 6

• Define and describe the human sex chromosomes.

Answer 6

• Pair of unmatched chromosomes that determine an
  individual’s sex
• males XY
• females XX
• X chromosome is 100 mb in length, 1000 genes.
• Y chromosome is 50 mb in length, only a handful of genes.

Question 7

• Describe the segregation of sex chromosomes into gametes.

Answer 7

• Meiosis in a female results in only x bearing eggs.
• meiosis in a male results in a 1:1 ratio of x and y bearing sperm.
• random fertilization results in a 50 50 chance of having a male or female.

Question 8

• Describe how X-linked genes and their respective traits are passed down to
offspring and know how to perform a Punnett square analysis on an X-linked
gene (separately and in conjunction with a gene that is not on an Xchromosome).

Answer 8

• first discovered on fruit flies by Thomas hunt Morgan.